Products of tetrafluorothanes

Abstract

This invention relates to a process for the production of 1,1,2,2- and/or 1,1,1,2-tetrafluoroethanes, and in particular to a process for the production of 1,1,1,2-tetrafluoroethane.

We claim: 
     
       1. A process for the production of 1,1,2,2-tetrafluoroethane which comprises contacting 1,1,2,2-tetrachloroethane with hydrogen fluoride in the vapour phase at a temperature in the range of about 200° C. to about 400° C. in the presence of a chromia based fluorination catalyst, the 1,1,2,2-tetrachloroethane being kept at a temperature below the reaction temperature before said contact and being vaporized for the reaction just prior to said contact in order to minimize the decomposition of 1,1,2,2-tetrachloroethane to trichloroethylene. 
     
     
       2. A process as claimed in claim 1 which includes the additional step of isomerizing the 1,1,2,2-tetrafluoroethane to 1,1,1,2-tetrafluoroethane. 
     
     
       3. A process as claimed in claim 1 wherein the hydrogen fluoride is present in stoichiometric excess with respect to the 1,1,2,2-tetrachloroethane. 
     
     
       4. A process as claimed in claim 1, 2 or 3 wherein the relative proportion of hydrogen fluoride to 1,1,2,2,tetrachloroethane is from 4:1 to 50:1. 
     
     
       5. A process as claimed in any one of claims 1 to 3 which is a vapour-phase process wherein the temperature is from 200° C. to 350° C. 
     
     
       6. A process as claimed in claim 1 wherein the fluorination catalyst is a zinc promoted chromia catalyst. 
     
     
       7. A vapour-phase process as claimed in claim 1 wherein 1,1,2,2-tetrachloroethane and trichloroethylene are co-fed as starting materials. 
     
     
       8. A process as claimed in claim 7 which comprises (A) contacting a mixture of 2-chloro-1,1,1-trifluoroethane and hydrogen fluoride with a fluorination catalyst at a temperature in the range from about 280° C. to about 450° C. in a first reaction zone to form a product containing 1,1,1,2-tetrafluoroethane and hydrogen chloride together with unreacted starting materials,   (B) passing product of step (A) together with trichloroethylene and 1,1,2,2-tetrachloroethane to a second reaction zone containing a fluorination catalyst at a temperature in the range from about 200° C. to about 400° C. but lower than the temperature in step (A) to form a product containing 2-chloro-1,1,1-trifluoroethane, 1,1,1,2-tetrafluoroethane, hydrogen chloride and unreacted starting materials,   (C) treating product of step (B) to separate 1,1,1,2-tetrafluoroethane and hydrogen chloride from 2-chloro-1,1,1-trifluoroethane, and unreacted starting materials, and   (D) feeding 2-chloro-1,1,1-trifluoroethane obtained from step (C) together with hydrogen fluoride to said first reaction zone (step A)   wherein 1,1,2,2-tetrachloroethane is fed to the process and partially fluorinated derivatives of the 1,1,2,2-tetrachloroethane are fed with the 2-chloro-1,1,1-trifluoroethane in step (D).   
     
     
       9. A process as claimed in claim 8 wherein the 1,1,2,2-tetrachloroethane is co-fed with the trichloroethylene in step (B). 
     
     
       10. A process for the production of 1,1,2,2-tetrafluoroethane and 1,1,1,2-tetrafluoroethane which comprises contacting 1,1,2,2-tetrachloroethane with hydrogen fluoride in the vapor phase in the presence of a zinc promoted chromia catalyst and at a temperature of 250° C.-350° C., the 1,1,2,2-tetrachloroethane being kept at a temperature below the reaction temperature before said contact and being vaporized for reaction just prior to said contact in order to minimize decomposition of the 1,1,2,2-tetrachloroethane to trichloroethylene.